This application is for support of the "4th International Workshop on Antigen Processing and Presentation" to be held at The Jackson Laboratory (TJL) in Bar Harbor Maine on September 16-19, 2004. The overall objective of this conference is to bring together leading investigators who have a common interest in the studies of antigen processing and presentation in relation to immune recognition. This conference provides a unique opportunity for established investigators and students to interact and share their unpublished results and exchange ideas. Researchers from Europe, Australia and North America will participate, creating a unique opportunity for scientific communication to keep pace with the discovery process and for fostering new research collaborations and partnerships. The meeting will include 6 platform sessions with particular emphasis on the structural and biochemical basis for antigen processing and presentation, as well as on the receptors involved in innate and adaptive immune recognition. A special session will be dedicated to interactions of the immune system and pathogens. In addition two sessions will cover the topics of physiology of the antigen presenting cells with an emphasis on their function in vivo, and on the physiology of the T cell responses to antigen stimulation. The format and size of this meeting is expected to promote a degree of interaction rarely found at larger conferences. The end result, based on our experience in the previous three Workshops, is that this kind of program gives rise to an impressive number of new ideas and collaborations. Postdoctoral and graduate students are encouraged to attend, and funds will be available to encourage students as well as women and underrepresented minorities to participate. This meeting has been held every two years since 1994 and continues to be unique and productive. [unreadable] [unreadable]